Following on these ideas, in the context of the Feynman path-integral fomulation, physicists considered homotopy classes of trajectories from initial to final particle configurations. Here one moves from the topology of physical space to that of configuration space. Schulman [1]} in 1968 proposed a model for the topological origin of particle spin. In 1971, Laidlaw and (Cécile) DeWitt [2]} deduced the topological origin of Fermi and Bose exchange statistics. In a footnote to their result, they remarked that in two space dimensions there seemed to be additional possibilites for quantum statistics, but they did not pursue this. In 1972, Dowker [3]} provided a more general discussion of quantum theory on multiply-connected spaces.
